The present invention relates to the depositing of thin films and more particularly to an ultra-high frequency device for depositing such thin films on solids.
Numerous applications at present use thin film deposits of different materials on solids. In order to obtain such deposits it is possible to use thermal phenomena in different types of ovens or furnaces. However, it is also possible to use electrical discharges in suitable low pressure gases and in particular high frequency discharges. At present, there is a complete range of depositing devices operating at different frequencies between 0 and 50 MHz for the thin film deposition of various materials on different types of supports.
For example, in order to obtain metal deposits, it is possible to use a vacuum bell jar into which a rare gas is introduced at a suitable pressure, for example argon at a pressure of 10.sup.-2 Torr. Two circular horizontal plates 30 cm apart are used for exciting an electric field at a frequency of 13.56 MHz, for example using a 500 W power generator. The material on which the deposit is to be made is fixed to the upper plate and sheets of metal, such as gold, platinum, titanium, tungsten, etc are placed on the lower plate. Metallic atoms bombarded by A.sup.+ argon ions produced by the gas discharge and present in the bell jar are deposited on the sample to be treated. The thus obtained deposits can be of the order of one to a few hundred Angstroms per minute and the properties of such deposits can be very good, both with regard to the purity of the deposit and its adhesion to the sample.
In other types of devices, a gaseous metallic composition is introduced at a suitable pressure into an enclosure in which is placed the material on which the deposit is to be made. An electric discharge of suitable frequency makes it possible to release the metal by decomposition of the gaseous mixture. As stated hereinbefore, the frequency range of the useful discharges extends up to about 50 MHz.
Moreover, there are other types of devices using ultra-high frequency discharges to obtain a surface cleaning action by erosion. The bombardment of chemically neutral species (rare gases) is used for this purpose. To obtain this effect, bombardment is carried out by high energy particles. Such ultra-high frequency discharges permit the bombardment of surfaces to be cleaned by erosion using ions which can reach very high energy levels, e.g. about 1 kV.